What this niddar is talking about has never been referenced in the puranas or the vedas, as for vajramushti that was performed using knuckle dusters/nakhas and was part of a wider training involved in indian wrestling. How do i know this you ask, i have many friends in southern and middle india who are linked to wrestling akharras that still practice this sort of art basically vajramusti.
Yes i agree that karas were used in form of strikes to the body but not really as this niddar is explaining....sorry mr niddar singh for ruining your fun.